PacketManager.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using System.Net;
using System.Net.Sockets;
using System;
using System.IO;

public class PacketManager : MonoBehaviour
{
    [SerializeField]
    string address;

    [SerializeField]
    int port;

    [SerializeField]
    uint mySelfId = 0;

    [SerializeField]
    GameObject mySelfObject = null;

    [SerializeField]
    GameObject enemyPrefab = null;

    Dictionary<uint, GameObject> players;

    Socket socket;
    IPEndPoint serverEndPoint;

    byte[] data;

    // Start is called before the first frame update
    void Start()
    {
        players = new Dictionary<uint, GameObject>();
        players[mySelfId] = gameObject;
        socket = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);
        serverEndPoint = new IPEndPoint(IPAddress.Parse(address), port);
        socket.Blocking = false;

        data = new byte[16];
    }

    // Update is called once per frame
    void Update()
    {
        for (int i = 0; i < 100; i++)
        {
            int rlen = -1;
            try
            {
                rlen = socket.Receive(data, data.Length, SocketFlags.None);
            }
            catch
            {
                break;
            }

            if (rlen == 16)
            {
                //MemoryStream ms = new MemoryStream(data, 0, rlen);
                //BinaryReader br = new BinaryReader(ms);
                
                uint playerId = BitConverter.ToUInt32(data, 0);
                float playerX = BitConverter.ToSingle(data, 4);
                float playerY = BitConverter.ToSingle(data, 8);
                float playerZ = BitConverter.ToSingle(data, 12);

                if (playerId == mySelfId)
                    continue;

                Vector3 playerPosition = new Vector3(playerX, playerY, playerZ);

                if (!players.ContainsKey(playerId))
                {
                    GameObject newPlayer = GameObject.Instantiate(enemyPrefab, playerPosition, Quaternion.identity);
                    newPlayer.GetComponentInChildren<TextMesh>().text = playerId.ToString();
                    players[playerId] = newPlayer;
                    newPlayer.name = string.Format("Player {0}", playerId);
                }
                else
                {
                    players[playerId].transform.position = playerPosition;// Vector3.Lerp(players[playerId].transform.position, playerPosition, Time.deltaTime);
                }
            }
        }

        Vector3 myPosition = mySelfObject.transform.position;

        /* byte[] dataId = BitConverter.GetBytes(mySelfId);
         byte[] dataX = BitConverter.GetBytes(myPosition.x);
         byte[] dataY = BitConverter.GetBytes(myPosition.y);
         byte[] dataZ = BitConverter.GetBytes(myPosition.z);

         dataId.CopyTo(data, 0);
         dataX.CopyTo(data, 4);
         dataY.CopyTo(data, 8);
         dataZ.CopyTo(data, 12);*/

        MemoryStream memoryStream = new MemoryStream();
        memoryStream.Position = 0;
        UnityBinaryWriter ubw = new UnityBinaryWriter();
        ubw.Write(mySelfId);
        ubw.Write(myPosition);
 
        byte[] outData = memoryStream.ToArray();

        socket.SendTo(outData, outData.Length, SocketFlags.None, serverEndPoint);

    }
}

class UnityBinaryWriter : BinaryWriter
{
    public void Write(Vector3 vec)
    {
        Write(vec.x);
        Write(vec.y);
        Write(vec.z);
    }
    
}